As air flows over a roof, the air attaches to the roof, and follows the contour of the roof up the incline, over the peak, and follows the contour of the roof on the other side. If the pitch of the roof is a standard 15 to 20 degree pitch, the wind attaches to the roof and climbs due to its own force over the building. Two factors contribute to the ventilation of a building: (1) the static pressure from within the building and (2) the outside wind pressure caused by wind flowing over the building. The static pressure is generally due to temperature differences between the floors, infiltration, air leakage, the building envelope heating and cooling, and heat generated by appliances, causing air to flow up through the roof of the building. The wind pressure is caused by the wind flowing over the building. The direction of the prevailing wind and the placement of the building dictate the need for ventilation. The amount of contact area of the roof with the wind also contributes.
A positive pressure area is created when the wind hits the roof and the building, while a negative pressure area is created on the opposite side. Within the negative pressure area, there is an area known as Z.sub.0, or the dead zone which is located just on the other side of the peak of the roof from the positive pressure area. Further down the roof is area Z.sub.1, or the recirculation area, which is adjacent the dead zone. Further down the opposite side of the roof from the direction in which the wind is hitting is area Z.sub.2, or the high turbulence zone. And yet even further down the roof line opposite the side being struck by the wind is area Z.sub.3, or the wake zone.
In order to most advantageously utilize the function of a roof ventilator, the goal is to place an inlet in the most positive pressure area, i.e. in the soffit next to the overhang, and on the face of the building which has air striking against it and being repelled away from it due to the high pressure occurring there. The next highest positive pressure zone is the area of the roof which is being struck by the wind, with a decreasing pressure as the wind flows up over the peak of the roof. For optimum use of a ventilator, an outlet should be located in the most negative pressure area. In the dead zone, the air has nearly zero velocity, with the velocity increasing as you go down the roof line on the opposite side from that face which is experiencing the wind.
Ideally, a ventilator will augment the static pressure and direct the wind flow without creating wind turbulence. Therefore, the vent should be located in the dead zone or in the recirculation region for maximum efficiency. Placing the vent in the dead zone also avoids infiltration because the substantially zero velocity of the air will not force any foreign matter back into the vent as the air is not moving in that region. In order to control infiltration, one must control the air around the placement of the vent.
It can be seen, therefore, that a single side leeway vent may be the most advantageous type of vent. Because vents cannot be customized for individual homes due to cost restraints, a vent should be designed for the average home, taking into consideration the direction of the prevailing wind in that area.
Roof ventilators permit circulation of hot air through the roof of a building to decrease the temperature within the building and to allow for air circulation under the roof, especially desirable for the removal of moisture build-up to prevent rotting of wooden members. Conventionally, roof ventilators have been unsightly, and have further served as nesting places for birds, insects and the like.
Some of the problems with previous roof ventilators have included a projecting height which is too great, multi-piece constructions which are difficult to install, roof ventilators which are unable to adapt to various roof pitches, thereby requiring a multitude of products for different building types and roof ventilators which are generally unsightly.
Furthermore, it has been found that roof ventilators must be of a sturdy construction to withstand pressures of shipping and handling, to avoid being easily damaged. Other considerations for shipping and handling include the ability of a design to provide a compact ventilator, one that can be shipped in a flat position, and one that can be stored in inclement weather conditions. The design of a roof ventilator must also include ways to improve aesthetics, propensity of air volume circulation, resistance to deterioration, ability to withstand exposure to high winds and other inclement weather conditions, along with its ability to prevent dirt, rain and insects from entering into the attic space being ventilated.
Previous inventions have included roof ridge ventilators which are placed on top of the shingles, such as U.S. Pat. No. 3,481,263 issued to M. C. Belden on Dec. 2, 1966 and U.S. Pat. No. 3,303,773 issued to L. L. Smith, et al., on Feb. 14, 1967. More recent inventions include roof ridge ventilators which are placed underneath cap shingles, for example, U.S. Pat. No. 3,236,170 issued to Meyer, et al., U.S. Pat. No. 4,280,399 issued to Joseph M. Cunning and U.S. Pat. No. 4,676,147 issued to the present inventor, John P. Mankowski.
U.S. Pat. No. 4,817,506 to Cashman discloses a ventilator having vertical struts to provide structural support. He further disclosed non-louver slit openings to permit air flow therethrough. However, the Cashman invention includes so many vertical struts that the net free area is greatly reduced, thereby impeding and restricting air flow by creating maximum restriction areas. The present invention achieves an even greater net free area by providing a roof ventilator having a sufficient structural static load bearing capability without the need for the vertical struts which so greatly reduce the net free area.
An object of the present invention is to provide an improved roof ventilator having particular utility in the construction of residential and commercial buildings.
Another object of the present invention is to provide an improved roof ventilator which will exhibit superior performance regardless of the orientation of the building.
Yet another object of the present invention is to direct air flow so as to reduce the velocity of the air flowing therethrough such as to limit entry of foreign particles through the roof into the ventilated space below.
It is yet still another object of the present invention to provide a roof ventilator which can easily be manufactured and easily installed.
The objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.